1. Field of the Invention
This invention is concerned with the stimulation of production of heavy oil.
2. Description of the Prior Art
Solvents have been injected into heavy oil wells in years past in order to improve production from those wells. Generally, the solvents used were light hydrocarbons, such as a rich gas, or light liquid hydrocarbons plus additives. These additives were for such purposes as dissolving deposited solid hydrocarbons or for breaking oil-water emulsions. Such mixtures were much more expensive than equal volumes of the crude they were designed to help produce. Reported results have indicated that well clean-up and emulsion reduction have been the primary mechanisms responsible for any increased production resulting from solvent injection. Production improvement as a result of the viscosity reduction due to solvent dilution has been discounted as a practical procedure.
It is the unexpected discovery of this invention that the production of heavy oil can be greatly increased by solvent dilution of heavy crude alone, the dilution resulting in a reduced viscosity of the solvent/crude mixture. The production increase is a result of proper design criteria of the solvent stimulation procedure, involving the volume of solvent used and the soak period prior to resumption of production. The continuity of production, once begun, is also important to the procedure. It has also been found that the same well can be solvent stimulated successfully many times, depending on the choice of proper intervals between solvent injections. In addition, it has been determined that relatively inexpensive hydrocarbons without additives, such as light crude oils, can be used as the solvent.